Opposum Lake Dam is a zoned rolled earthfill dam with an impervious core. Construction was completed in June 1961. It was inspected 5 April 1978. This dam does not have the capacity to pass the recommended spillway design flood of one-half the Probable Maximum Flood without overtopping. The spillway capacity is not considered seriously inadequate, as the project will pass the 100-year flood. A serious and persistent problem exists in a constant seepage passage over most of the length of the downstream slope of the dam. It is recommended that the owner maintain continual surveillance of the dam until the embankment has been rehabilitated to correct the serious seepage problem.